Induction of puberty and fertility of Brahman-influenced heifers exposed to progesterone prior to artificial insemination

• Grant number: 19/21650-0
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: November 30, 2019
• End date: March 22, 2020
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Animal Reproduction
• Principal Investigator: Guilherme Pugliesi
• Grantee: Leonardo Marin Ferreira Pinto
• Supervisor: Mario Binelli
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: University of Florida, Gainesville (UF), United States
• Associated to the scholarship: 18/25393-9 - Abundance of transcript for receptors of type I interferon in blood leucocytes during early pregnancy in Nelore heifers, BP.IC

Abstract

The animal protein production represents an important factor on food production. Thus, it is required that livestock herds have better indexes on efficiency production, which could be achieved by the use of technology and biotechnologies applied to genetic improvement, well-being, nutrition, health and reproduction, linked to the economic and environmental sustainability of the sector. Breeding success is related to sexual precocity and service period of females, which differ between genetics (Bos indicus vs. Bos Taurus). Regarding sexual precocity, animals must be able to reach puberty earlier and, consequently, to produce more calves throughout their productive life. In this regard, hormonal induction of heifers' puberty and fertility could be a strategy to be adopted. Several studies discuss the use of progesterone (P4) as a cyclic inducer in heifers, as it stimulates the release of GnRH by the hypothalamus leading to activation of the hypothalamus-pituitary-gonadal axis and reproductive development of these females. However, it has been shown that Bos Taurus, by different physiological conditions, reach puberty earlier than in mixed-breed or Bos indicus Thus, this project aims to study the use of an intravaginal P4 device (CIDR) on the induction of puberty of pre-pubertal Brahman heifers and its effects on fertility rate under tropical and subtropical conditions found in Florida (USA), when compared to pubertal heifers submitted to FTAI. For this purpose, 570 beefs heifers, will be used, and day of FTAI will be defined as D0. The heifers will be evaluated by B-mode ultrasonography on days D-33, D-23, D-3 and D30On D-33, body weight (BW), body condition score. (BCS), reproductive tract score (RTS), ovaries and puberty status will be measured. Then, based on these evaluations, the females will be divided in two categories: pubertal and pre-pubertal. Each category will have two groups: females that received or not the intravaginal progesterone devices on D-23. On D-13, the devices will be removed, and all heifers will receive a dose of prostaglandin F2a analogue (PGF2a) and heat detector patches. On D-9, all heifers will receive a GnRH dose and the CIDR. CIDRs will be removed on D-3, along with another PGF2a dose and heat detector patches insertion. Insemination will be executed 84 hours after CIDR removal (D0), and the females will also receive a dose of GnRH. On D30, pregnancy diagnosis will be conducted by transrectal ultrasonography. It is expected that pre-pubertal heifers will have same fertility rates as the pubertal heifers. (AU)